Chad I think it would have to do with where you were when engaging the mob.

Say you are inside the gas station like in one of the mob videos and the mob decides you're next. Hopefully you have some environmental assistance in the form of shelves, displays, etc. Most gas stations have one main door and a back door. I would be trying to get to that back door.

From some of the videos though they very quickly fill and surround the store before the owners or patrons really know whats going on.

If I had to shoot, it would be only against what was between me and leaving. Understanding that once it is known you have a gun and are trying to leave, the mob could focus its entire attention on you. So I would shoot only if I had to and wouldn't harass the mob, especially if I were so far unnoticed, by firing at random thugs. I would simply leave as fast as I could.